Koji squid with Ponzu mayonnaise as seen in San Francisco, California, on May 15, 2013. Food styled by Tara Duggan.

Koji squid with Ponzu mayonnaise as seen in San Francisco, California, on May 15, 2013. Food styled by Tara Duggan.

Photo: Craig Lee, Special To The Chronicle

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Koji-marinated asparagus with lemon zest as seen in San Francisco, California, on May 8, 2013. Food styled by Tara Duggan.

Koji-marinated asparagus with lemon zest as seen in San Francisco, California, on May 8, 2013. Food styled by Tara Duggan.

Photo: Craig Lee, Special To The Chronicle

Traditional Japanese koji turns into versatile seasoning

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There's a new secret sauce in town. It adds an umami punch to vegetables and fish, it tenderizes meat and it gives roast chicken a golden glow. It allows you to use less salt, less sugar and less fat. And it has nothing to do with MSG.

It's koji. An ingredient that has been used for centuries in Japan to make soy sauce, sake and miso, it's now been reborn as a seasoning base for marinades, sauces, salad dressings and pickles.

When koji - essentially, rice that's been inoculated with the koji mold - is combined with water and salt and allowed to ferment, it turns into shio-koji or salt koji, a seemingly magical sauce that thrills cooks with its flavor-boosting abilities.

"It's amazing," says Nick Balla, executive chef of San Francisco's Bar Tartine, which is hosting a koji-themed dinner on May 28. Balla and his cooks make koji in-house to use in pickled vegetables and to marinate whole chicken before roasting.

"It seasons and sweetens the meat and crisps the skin, and it has this miso-like aroma," says Balla.

After seeing a resurgence in Japan in the last year or two, koji is making inroads with Bay Area chefs, and is becoming available in Japanese markets and from a few California producers.

Sold refrigerated to stop fermentation, salt koji is a creamy sauce that's ready to add to meat, seafood, vegetables and other foods before cooking.

Flavor without fuss

"It makes the umami come out so nicely, so you don't need too many ingredients to make it tastier. You don't have to do anything," says Yuko Hayashi, owner of Izakaya Yuzuki in San Francisco, which has a koji-themed menu and uses the seasoning in chicken yakitori, air-dried horse mackerel and grilled squid.

In The Chronicle's test kitchen and at home, we loved how koji adds a savory depth and sweetness all at once, simplifying basic recipes.

For Balla's roast chicken (see recipe), we rubbed the bird all over and under the skin with salt koji and refrigerated it uncovered, overnight. The chicken came out bronzed and crisp outside, but it stayed juicy inside and was infused with salty, soy flavor.

In a vinaigrette, the salt koji balanced the acidity of the vinegar, allowing us to use a lot less olive oil. We also loved what koji did to blackberry preserves, bringing out the flavor of the berries with very little sugar.

Make it yourself

The only downside is that prepared salt koji is expensive, so it's more economical to make it yourself, starting with dry granulated koji and fermenting it for seven to 10 days (see accompanying instructions).

Koji-marinated foods can burn easily because koji produces enzymes that transform starches into sugar. It also causes proteins to break down, creating glutamic acid, which is what gives umami to foods.

Because of that chemical process, salt koji brings out a much wider range of flavors than plain salt can. Although it is not necessarily low in sodium, you definitely won't need to add extra salt when you use salt koji in recipes, and you can serve these deeply flavored dishes with a simple bowl of unseasoned rice.

Mariko Grady, the granddaughter of a miso maker from Japan, debuted Aedan, a line of fresh koji-based products, at the Ferry Plaza Farmers Market last month. At her shared cooking space in La Cocina in San Francisco, she demonstrated how she starts a batch of fresh koji.

Grady steams Koda organic rice, grown in the Central Valley, for seven minutes to soften it, then sprinkles it with powdered Aspergillus oryzae, the koji mold. She incubates the rice by wrapping towels around the container for 24 hours. At this point, the koji starts to generate its own heat, so she monitors it to make sure it doesn't get too warm and then allows it to incubate another 24 hours.

Fresh and fermented

The result is fresh koji, which she uses to make miso and amazake, the fermented rice drink. She also sells fresh salt koji, which she says is higher in enzymes than the packaged kind sold in Japanese markets.

"I'm happy to share this Japanese tradition," she says. "A lot of customers haven't heard of it, but when I tell them the health benefits, they're interested."

Bar Tartine started out using commercial koji in several dishes, but because the restaurant specializes in house-made fermented foods, co-chef Cortney Burns learned how to make koji, too. She consulted often with chef Takashi Saito of Izakaya Yuzuki, which is just a few blocks away.

"We were very fortunate. The first time we tried to inoculate rice it kojied," says Burns, who often uses the Japanese noun as a verb.

The restaurant now makes 20-pound batches of koji at a time, including versions made with white sushi rice, pearl barley and brown rice. They also use their koji to make rice vinegar and in miso made with flageolet beans, lima beans and sprouted lentils.

For their koji dinner later this month, Burns and Balla invited Myoho Asari, the owner of Kojiya Honten in Japan, an artisan koji maker in Japan's Oita Prefecture. Asari's company has produced koji for sake and miso producers for three centuries, but when its business lagged, along with the Japanese consumption of these traditional foods, it began promoting salt koji as a cooking ingredient.

'I'm addicted'

Sonoko Sakai, a Los Angeles cooking teacher and writer, will be a guest chef at the dinner, presenting her handmade soba noodles with a koji-infused sauce.

"Now I'm addicted" to koji, says Sakai. "It's my hidden ingredient."

The founder of Common Grains, an organization that promotes Japanese cooking and culture in the United States, Sakai helped arrange Asari's visit the United States.

"I really advocate this movement of going back to the past and learning about our heritage and foods like koji, which is so basic in our cuisine," says Sakai.

"Now we're shedding a new light on this ingredient and making it accessible in another way."

Tasting koji

Bar Tartine: A koji-themed dinner is scheduled for May 28 with guests Myoho Asari, owner of Kojiya Konten in Japan, and Sonoko Sakai, founder of Common Grains in Los Angeles.

Tickets are $85, not including tax and gratuity. For reservations, call (415) 487-1600. Bar Tartine is at 561 Valencia St. (near 16th Street), S.F. www.bartartine.com.

Izakaya Yuzuki: This Mission District izakaya has a koji-themed menu, which features several dishes prepared with salt koji. 598 Guerrero St. (at 18th Street), S.F.; (415) 556-9898. www.yuzukisf.com.

- Tara Duggan

Cooking with koji

Where to find it

Koji is available in a few forms. You can find the prepared sauce, called shio-koji or salt koji (above left and center), in the refrigerated section of Japanese markets for $4-$5 for 4 to 16 ounces, depending on the brand.

Japanese markets also sell granular rice koji, such as the U.S.-made Cold Mountain brand, (above right), which you can use to make your own salt koji. Instructions are included to add water and salt and let the mixture ferment, loosely covered, at room temperature for seven to 10 days.It's $7 per 20-ounce container.

The amount of salt koji to use depends on the weight of the main ingredient, and it's much easier to figure out in metric (most digital food scales convert to metric). The ratio is 10:1, so for every 100 grams (3.5 ounces) of food, use 10 grams (1 1/2 teaspoons) salt koji, or 10 percent of the total weight of the food. For example, a 7-ounce piece of salmon requires 1 tablespoon salt koji.

Instructions: In a shallow bowl or baking dish, toss the asparagus in the koji and let marinate for 20 minutes.

Heat the olive oil in a medium frying pan over high heat. When the oil shimmers, add the asparagus and saute 3 minutes. Stir in the lemon zest and pepper; cook 1 minute more. Stir in the lemon juice, remove from the heat and serve immediately.

Grilled Koji-Marinated Hokkaido Squid With Ponzu Mayonnaise

Serves 4

This recipe is from Takashi Saito of Izakaya Yuzuki in San Francisco. In addition to the koji, look for yuzu juice, ponzu (citrus soy sauce), yuzukosho (a yuzu-green chile paste) and shichimi togarashi (red pepper mix) in Japanese markets. Specialty seafood markets sell large whole squid, sometimes frozen, but if you can't find it you can use what's labeled calamari - ask for the bodies because the tentacles are sometimes too small to grill.

Squid

2 pounds whole uncleaned squid (2 large squid) or 18 ounces cleaned squid; if very small, just use the bodies

2 1/2 tablespoons pureed salt koji

Ponzu Mayonnaise

1 egg yolk

1/2 teaspoon Dijon mustard

8 ounces vegetable oil

-- Pinch ground black pepper

2 tablespoons yuzu juice or yuzu seasoning

2 tablespoons ponzu

1/2 teaspoon yuzukosho (optional)

-- Shichimi togarashi, to serve

To marinate the squid: If using uncleaned squid, separate the tentacles from the mantle (body). Remove the beak from the tentacles and the internal organs and cartilage from the inside of the mantle; rinse thoroughly. Peel off all the skin from the mantle and dry with a paper towel.

Rub the salt koji onto the surface of the squid, including the tentacles, or the calamari bodies. Store in a zip-top bag or other airtight container at least 3 hours or overnight.

To make the mayonnaise: Whisk together the egg yolk and mustard in a medium bowl. Starting drop by drop, slowly whisk in the oil until you have an emulsion, then pour in a steady stream while whisking to make a mayonnaise. Whisk in the yuzu juice, season with pepper, cover and refrigerate until set.

Before serving, combine the ponzu and yuzukosho in a small bowl. Whisk it into the mayonnaise, then transfer to a serving bowl. Sprinkle shichimi togarashi on top.

To grill the squid: Preheat a grill to medium high.

Remove the squid from the container and grill it whole - do not clean off the salt koji - until browned and opaque, 3-4 minutes per side. If using smaller calamari, skewer and cook about 2 minutes per side.

Cut the squid into thin slices, if large, and serve with the Ponzu Mayonnaise.

Koji-Pickled Cucumbers

Serves 2 to 4

This recipe was adapted from Kojiya Honten, an artisan koji maker in Japan. You can use any other vegetable that is commonly used for tsukemono (Japanese-style pickles) such as carrots, daikon radish, turnips or cabbage. Use 1 tablespoon salt koji for every 100 grams (3 1/2 ounces) vegetables.

7 ounces Japanese cucumbers (2 small cucumbers)

2 tablespoons pureed salt koji

Instructions: Wash the cucumbers and cut into chunks.

Put the salt koji in a zip-top bag and add the cucumbers. Mix together by rubbing lightly. Refrigerate overnight.

Remove the cucumbers from the bag and squeeze lightly. It isn't necessary to rinse off the salt koji. Drain the liquid and serve as a condiment for rice.

Nutrition information: The calories and other nutrients absorbed from brines vary and are difficult to estimate. Therefore, this recipe contains no analysis.

Koji-Marinated Roast Chicken

Serves 4 to 6

From Bar Tartine chefs Nick Balla and Cortney Burns, this roast chicken comes out savory and juicy, with a crisp skin. All it takes is rubbing a whole chicken with koji and marinating it in the refrigerator, uncovered, for up to 48 hours before roasting. Do not use your oven's convection setting, because the natural sugars in the koji will cause the skin to brown more than a plain roast chicken, but it will not burn if watched closely. Serve with the Sauteed Lemon-Koji Asparagus.

1 whole chicken, 3-4 pounds

1/2 cup pureed salt koji

Instructions: Rinse the chicken and pat dry. Tuck the wing bones back and rub the entire chicken with the salt koji paste. Lift up the skin at the top of the neck and rub the salt koji onto the chicken breast and under the skin, working as far down as you can to legs if possible. Refrigerate, uncovered, 3 to 48 hours in the refrigerator to dry out a bit.

Preheat the oven to 350°. Pull the chicken from the refrigerator 30 minutes before cooking to temper the meat. Place the chicken, breast side up, on a rack, tie the legs and roast until the internal temperature taken in the thigh reaches 155°, 60-90 minutes, depending on the size of the chicken (estimate 20 minutes per pound or more). Turn the chicken occasionally to encourage even cooking.

Remove from the oven and tent the chicken with foil. Let rest at least 15 minutes; the chicken will continue to cook for a bit, raising its internal temperature to 165°.

Lift the chicken to drain its juices from the cavity into the pan. Remove the chicken from the hot pan to stop the cooking process, and place on a platter. Reserve drippings to slather on bread or as a dip for the chicken meat. Carve the chicken and serve.

Koji Shira-ae With Favas & Tomatoes

Serves 4

Shira-ae is a classic tofu dish in which a single vegetable, or a combination of two or three, is tossed with seasoned mashed tofu. In this recipe from Sonoko Sakai, tofu is first marinated in salt koji for two to three days and then seasoned with nerigoma, Japanese roasted sesame seed paste, to make a mild and creamy dressing. You will have koji tofu leftover that you can use to make more shira-ae. Other vegetables you can use include cooked asparagus, snow peas, green beans, mushrooms, carrots and eggplant; the shira-ae also works with fruit or as a vegetable dip.

Koji Tofu

14 ounces soft or silken tofu

2 tablespoons pureed salt koji

Shira-ae

1 cup shelled fava beans, from about 1 pound in the pod

1 tablespoon nerigoma (Japanese sesame seed paste, see Note)

1 teaspoon sugar

1 pint cherry tomatoes, halved lengthwise

For the koji tofu: Wrap tofu with paper towels or a dish towel, and place it on a rimmed baking sheet. Put a cutting board on top of the tofu and let sit for about 20 minutes. Lightly pat tofu with a dish cloth to dry the surface.

Slice tofu crosswise into three pieces. Baste the tofu pieces with the salt koji, then place some of the extra salt koji in the bottom of a container. Add the tofu, cover, drizzle with any extra koji, and refrigerate at least 2-3 days. Use within 7-10 days.

For the shira-ae: Bring a large pot of salted water to a boil. Add the fava beans and cook until just tender, about 3 minutes. Drain and shock in ice water. Remove outer skins of the fava beans.

Place one slice of the koji tofu in a medium bowl and mash with a fork. Add the nerigoma and sugar; mix well until creamy. The dressing is best used right away, but will stay fresh in the refrigerator for one day.

Combine the tomatoes and fava beans in a medium bowl; toss with the shira-ae dressing, and serve immediately.

Note: Nerigoma, available in Japanese markets, is a paste made with roasted sesame seeds that's similar to tahini, but more fragrant. You can substitute unsalted tahini.

Nutrition information: The calories and other nutrients absorbed from marinades vary and are difficult to estimate. Therefore, this recipe contains no analysis.

Koji Blackberry Preserves

Makes 1 1/2 cups

More of a topping than a jam, this version of fruit preserves adapted from Japanese koji maker Kojiya Honten is low in sugar and lightly cooked, allowing the flavor of the blackberries to come through. With its slight savoriness, the preserves would be just as good over cornmeal pancakes as with pork chops.

12 ounces blackberries

3 1/2 tablespoons golden brown sugar

1 teaspoon pureed salt koji

Instructions: Combine all the ingredients in a heavy-bottom medium pot.

Koji Vinaigrette

Makes 1/2 cup

Adapted from a recipe by Makiko Itoh in "The Japan Times," this brilliant salad dressing uses about one-third of the amount of oil called for in most vinaigrettes, because the koji balances out the vinegar and adds savoriness.

3 tablespoons pureed salt koji

3 tablespoons red wine vinegar

3 tablespoons extra virgin olive oil

1 1/2 tablespoons rice vinegar

1/2 teaspoon finely grated fresh ginger (optional)

-- Freshly ground black pepper

Instructions: Whisk together all the ingredients in a small bowl, or puree in a blender. Use as you would any vinaigrette, and store in the refrigerator up to 1 week.